This invention generally relates to the art of electrical interconnections and, particularly, to a system for facilitating the interconnection of the conductors of flat circuits, such as flat flexible circuits, along with a method of fabricating such flat circuits.
A flat flexible circuit conventionally includes an elongated flat flexible dielectric substrate having laterally spaced, generally parallel strips or conductors on one or both sides thereof The conductors typically are covered with a thin, flexible protective layer or film on one or both sides of the circuit. If films are used on both sides, the film on one side forms the substrate. Cutouts or openings are formed in the top film to expose the underlying conductors typically at the end of the circuit where the conductors are to engage the conductors or terminals of a complementary mating connecting device which may be a second flat flexible circuit, a printed circuit board, discrete electrical wires or the terminals of a mating connector.
These preformed flat circuits, with their cutouts or openings to expose the conductors, then are transferred or transported to other locations where the conductors are interconnected to the conductors or terminals of the complementary mating connecting device by soldering processes. During soldering, solder material is added to permanently interconnect the conductors of the flat circuit to the conductors of the mating connecting device. The preformed flat circuits may be transferred to inventory and subsequently transported to the manufacturing, interconnecting or soldering processing locations.
Problems are encountered in the fabrication and interconnection procedures of the prior art as described above. For instance, applying solder material to the conductors of the flat circuits in the processing operations are very expensive and difficult to control. Skipped or insufficient solder material could lead to quality disasters. It is very difficult and expensive to inspect the quality of solder joints involving flat circuits, particularly when a flat circuit is interconnected to a second flat circuit at a xe2x80x9clap solder jointxe2x80x9d. The present invention is directed to solving these problems by incorporating the application of the solder material in the primary fabrication process of the flat circuits and, thereby, assuring proper solder material presence prior to the actual soldering process.
An object, therefore, of the invention is to provide a new system for facilitating the interconnection of the conductors of a flat circuit, such as interconnecting the conductors of a pair of flat circuits.
Another object of the invention is to provide a new method of fabricating and interconnecting the conductors of a pair of flat circuits.
A further object of the invention is to provide a new method of fabricating a flat circuit.
In the exemplary embodiments of the invention, a flat circuit, such as a flat flexible circuit, is provided with a plurality of conductors covered by a dielectric film. An opening is formed in the film to selectively expose the conductors. A layer of solder material is applied on the exposed conductors in the opening. Therefore, the opening can be juxtaposed with a mating conductor to facilitate interconnecting the conductors by an appropriate soldering process using the preapplied solder material.
According to the invention, a second flat circuit may be provided with a plurality of conductors covered by a dielectric film, with an opening in the film to selectively expose the conductors. A layer of solder material is applied on the exposed conductors in the opening of the second flat circuit. The two flat circuits can be overlapped with the openings in the respective dielectric films thereof in juxtaposition. The conductors of the two circuits then can be easily soldered through the juxtaposed openings using the preapplied solder material on the conductors of both flat circuits.
According to various aspects of the invention, the opening in the dielectric film of the preformed flat circuit can be located at a distal end of the circuit, or spaced inwardly from the distal end. The opening may comprise a window surrounded by the film. In fact, a plurality of the windows can be provided in a predetermined pattern in the film. In all of these embodiments, electrically interconnecting the flat circuit is facilitated by having solder material preapplied to the conductors within the film opening(s) regardless of the location thereof.
According to another aspect of the invention, the solder material may comprise a layer of solder covered by a layer of flux. The solder and flux layers are preapplied to the conductors within the openings in the dielectric film of the flat circuit. The flat circuit may be a flexible flat circuit using a thin, flexible protective film on both sides of the circuit.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings.